Thanks so much for your time and help.
Sorry, I understand that the error message should be hidden by default and that JS would be showing it when it feels it is necessary. I guess my question is - what configurations do I have to make in DNN so that it knows what that necessary condition is? I want to tell it , "not only is this field required, but you must pick the TRUE option and not the FALSE option for this to be considered a valid form." Is that what selecting a TRUE/FALSE required custom field does by default?
By "enable show script errors," do you mean have the developer tools open in the browser and show the console tab? If so, I am doing that with Chrome and not getting any errors logged to the console. I have just verified that this is also the case for Firefox and IE. If you meant something different, how do I go about doing what you're saying?
I think a good next step would be to try disabling any external JS references one by one and see if I can isolate the cause. If you can think of anything else I need to configure DNN-wise, please let me know.